This invention relates generally to tools, and more particularly, to torque wrenches.
As is well known in the art, when an internally threaded member (e.g., a nut) is tightened onto an externally threaded member (e.g., a bolt), the bolt tends to undergo a substantial amount of twist (e.g., stress) adjacent its interface with the nut. This stress may at times be great enough to cause the bolt to fracture or otherwise become damaged therealong.
The instant invention involves a compensating torque wrench tool which is arranged to substantially reduce this stress during the tightening process by rotating the nut in a first rotational direction, while at the same time rotating the associated bolt in the opposite rotational direction. The device further includes means for measuring and indicating the amount of torque being applied to the nut and bolt, respectively.
In the prior art various types of torque wrenches have been disclosed. Some of such wrenches, include bolt tensioning means and/or torque measuring means.
One such device is disclosed in the U.S. Pat. No. 2,760,393 (Stough). The Stough device is used for pre-tensioning a bolt and tightening a nut thereon. A first portion of the device engages the free end of the bolt so as to produce a predetermined amount of axial tension on the bolt, without applying any torque or twisting action to the bolt. A second portion of the device rotates the nut onto the bolt while the bolt is being pre-tensioned as just described. The device further includes tension indicator means to measure the amount of axial tension being applied to the bolt.
Another prior art device, this one designed to simultaneously rotate a bolt in a first rotational direction and a nut in the opposite rotational direction is manufactured and sold by Ingersoll-Rand Corporation, is illustrated in a sales brochure published by Bethlehem Steel Corporation, of Lebanon, Pennsylvania. The device is used in combination with a specially constructed bolt which is manufactured and sold by Bethlehem Steel. In that regard, a 12-point spline (i.e., a gear-like member) is frangibly secured, axially to the free end of the bolt. In order to tighten the nut to the bolt, the torque wrench engages and rotates the nut in a clockwise direction while at the same time engaging the spline with a socket-like member and rotating it, together with the bolt, in the opposite direction, until the torque is sufficiently great to cause the spline to fracture free from the bolt.
The Ingersoll-Rand device does not include force measuring means, nor does it include means for tightening the nut to the bolt at a tension other than the tension causing the spline to fracture free from the bolt.
Furthermore, the device requires the use of a rather intricately constructed and probably expensive bolt, whose frangible spline would preclude the bolt from being re-used.
Various other types of torque wrenches, some of which include force measuring means, are disclosed in the following U.S. Pat. Nos. 2,888,825 (Krafft); 3,643,501 (Pauley); 4,212,196 (Krieger); 4,226,127 (Hardiman) and 4,274,310 (Michaud). However, it should be pointed out that none of the above identified patents disclose a torque wrench capable of rotating the bolt in a rotational direction opposite to that of the nut.